First and foremost, get your soil tested. Your state co-operative extension service will do it for you at a cost of about $20-25. Most soils do not need Mg which is the metal part of Epson salts.

I'm broke. That's more than I want to spend right now on testing soil.

Also, I mainly use it for potted plants.

Sorry to hear your broke! Epson salts has only shown to increase the 'green' color of evergreens but no reason for this phenomenon has been determined. Based on this, I wouldn't bother using ES and save it for a southing bath.

It's a source of magnesium and sulfur - the Epsom Salt Council (whatever that is :)) suggests 2 T dissolved in a gallon of water for indoor plants, you then use that solution to water your plants. I've seen that same amount - 2 T dissolved in water suggested as a foliar spray for rhododendrons with yellowish leaves - greening of the shrubs following the spray will help determine if lack of magnesium rather than lack of iron is contributing to the off color and appropriate longer term steps can then be taken.

I haven't used it in containerized plants, my plants haven't shown a need for additional magnesium...I normally use a water soluble all purpose fertilizer like Peters when I fertilize, mixed to only about half the strength recommended on the label for mature plants in containers, even less for seedlings and young plants.

"A lack of magnesium is characterized similarly with iron deficiency but the older leaves, generally at the bottom of the plant, show marginal and interveinal reddening or yellowing with leaf base and midrib staying green. Later in the season interveinal necrosis may occur. Leaves may be brittle and thin with leaf curling and stunted growth"

In addition to the aforementioned attributes, I do seem to recall Paul James (who has a chemestry degree) mentioning on his show that epson salt helps counter the ill effects of salt buildup from synthetic fertilizers. Regardless, if your soil is not lacking in Mg adding epson salts could actually harm the plants. Probably best to do as morz8 suggests and try it as a foliar spray first.

tj

Since Epsom Salts are a source of a very soluble form of magnesium using it in any amount in soils or on plants (foliar sprays) can create more problems than it would solve. An excess of magnesium can prevent plants from uptaking other necessary nutrients which means you will not have strong and healthy plants.

"An excess of magnesium can prevent plants from uptaking other necessary nutrients"

True, you can upset the Calcium/Magnesium ratio if too much Magnesium is added to the potting soil...but this does not apply to foliar applications, it would not be interacting with nutrients "in" the potting soil.....

Schmoo

Why would a foliar applcation not adversly affect the nutrient balance in a plant, unless foliar feeding does not work?

Although foliar uptake in lower, the Mg is absorbed and utilized at the point of need. Because of the physical characteristics of each chemical element, each element has an effect on other elements in a solution (moist soil is a solution). If you want an in depth explanation, get a Chemistry book and read the section of 'electronegativity'.

ms minnamouse, I try to determine that a deficiency exists before applying a remedy; for me, the symptom of Mg. deficiency is a darker green triangle at the leaf base. The triangular pattern follows the outline of the leaf itself but can appear compressed from apex to base. It is best seen on the older leaves on the Canary Is. date palm. Some authorities say that Mg. is a freely mobile element and Mother Nature, conserving as She is, will draw it out of the older leaves before they are shed. They recommend that Mg. deficiency be corrected only when the younger leaves display the symptoms. The deficiency is often linked to unfavorable pH in the soil and the easiest way of correcting it is by foliar application (rather than pH correction). Foliar uptake of any nutrient is very different from root assimilation, so please observe all label directions.
For soil mixes used in container growing, my best suggestion would be to read the relevant posts on this forum by tapla.
Full disclosure statement. I have not received any compensation (cash or kind) or promise of High Office from said tapla....etc. etc.

So if you spray an excess of one nutrient on the foliage of any plant that will not inhibit the utilization of other nutrients? Aside from the fact that the studies used to support foliar feeding have been found to be flawed, you can still cause plant health problems by feeding a plant too much of one nutrient, no matter the method. Plant nutrition is not unlike human nutrition, if you attempted to subsist on a diet of Twinkies and soda pop bad thing would happen to you.

kimmsr, yes within the leaf. Get yourself a good book on Soil Science and read it so you have a better understanding of nutrient (chemical elements) interaction and root uptake.

ms minnamouse, I just want to clear up a few points that I may have missed.
I did not wish to suggest that it is possible to provide ALL the nutrients needed by a plant by foliar application alone. My experience has taught me that this is not possible.
Magnesium is a major element in plant nutrition and it is one that can be supplied as a foliar spray. Because the process of uptake through the leaf is very different from uptake by roots, very great care must be taken when applying any foliar spray.
Nutrition of container-grown plants is not quite the same as for plants grown inground outside.
'tapla' has shared a great deal of experiential knowledge on container mixes on the 'Container Plants' forum.

As I stated earlier there are many soil scientists that believe the research that foliar feeding is based upon is flawed. That conclusion comes from reading lots of good books on soil science.

kimmsr, Please provide me with a list of at least three of the books you reference. Please include: title, author, publisher and copy right date. I'm very interested in learning about these new findings. Thanks, petzold6596

kimmsr,

I also would be interested in what books/papers/research work/soil scientists you are refering too.

_minnamouse,

Back to your question...if you have used a "pinch" and not seen a problem, why change??...plants don't read our books:-)). (Mag. is very soluble, most folks rely on dolomitic lime as a source, if that is not in your potting soil, your plants could probably use some). Find a happy medium between what you have been doing and the label rate...once a month or so. If people have scared you about using Epsom salts, try a foliar spray at the same rates (Mag.toxicity is RARE, normally happens in mineral soils with naturally high mag. content)...almost all references to nutrient toxicity/antagonisum are based on what happens in the soil, NOT foliar applied!!. Whether the roots or the foilage, low dose moderation is normally safe...just research it a bit before changing what you have been doing.

Schmoo

Far too many over far too many years to remember, although Chalker-Smith comes to mind right off.

kimmsr, Thanks for the name. I just finished reading two of 'Myth' publications and in neither did she make a definitive statement that all foliar spraying was ineffective. In fact she stated that it is a very effective method of applying micronutrients to many plants that exhibit deficiencies of these nutrients because of high concentration of soil K (potassium). Dr. Chalker-Smith sites the work of Dr. Tukey, Michigan State U., your home state Ag. school, pertaining to the positive up take of micronutrients in leaves. All sited references did state that the rate of absorption was effected by the anatomical make up of the leaf.

I suggest you reread these publications, if for nothing more than to refresh you memory of the facts.

Since ms_minnamouse is "broke" and Epsom salts are inexpensive, the danger is that she will apply too much and do harm to her plants.

Referring to the quote from the message above by morz8,

"the Epsom Salt Council (whatever that is :)) suggests 2 T dissolved in a gallon of water for indoor plants"

That seems too strong to me for the prudent use of Epsom salts. I personally think it is error prone to use a single letter abbreviation for teaspoon and tablespoon. I prefer tsp for teaspoon and tbs for tablespoon. The "T" used above indicates tablespoon (a "t" would indicate a teaspoon), and two tablespoons per gallon is, in my opinion, much too strong for a foliar spray of inorganic nutrients (including magnesium sulfate) and probably too strong for a soil application. If you were feeding sugar in a foliar spray, that much sugar might be appropriate.

My favorite single reference book for plant nutrition is currently the Handbook of Plant Nutrition edited by Allen V. Barker and David J. Pilbeam, published by CRC Press in 2007. I found its information on the role of silicon in plant nutrition to be particularly helpful. And its recent publication date indicates that its information is reasonably "up to date".

ZM

minnamouse,

I did a little digging and came up with a rate you may find suitable.
The rate recommended by the "Epsom Salt Council" and a lot of others (2 tablespoons per gallon)is twice as high as what is used & recommended in commercial horticulture/floriculture.
Current recommendations (NCSU, Auburn and other universities with strong horticultural/floriculture programs) are 2 lbs. per 100 gallons of water, this breaks down too a "light??" tablespoon (1 tbsp. Epsom Salt= 11+ grams...the 2 lbs. rate breaks down to about 9 grams)per gallon of water.

Schmoo

I have used epsom salts to invigorate my palm trees and my begonias: it is the magnesium that they like. As with all things, use it in moderation. I use about a handful in a 2 gallon bucket and then water it in well.

I have heard that you can just sprinkle it too, but have never tried that.

Naturally I bath in it too for the sore muscles I get after gardening.

I used a handful mixed in the soil under all my tomato plants and they have benefited tremendously from the addition compared to last years plants. I'm sure it depends on the plant it's being used on as to how much is beneficial.